A method includes a first molding process and a second molding process performed repeatedly. The first molding process includes injecting resin into a first pair of molds, in which a first pair of divided pieces is formed and which is fitted together without an inner mold, to couple the first pair of divided pieces to form a first hollow article at an injection station. The second molding process includes (i) injecting resin into a third pair of molds, which is fitted together with one inner mold interposed therebetween, to mold a third pair of divided pieces at the injection station, (ii) taking out the first hollow article from the first pair of molds at a removing station, and (iii) removing another inner mold from a second pair of molds while leaving a second pair of divided pieces between the second pair of molds at the setup station.